FIG. 1 depicts a schematic diagram of a portion of a typical wireless communications system in the prior art. Such a system provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals 101-1 through 103-1) that are situated within a geographic region.
The heart of a typical wireless telecommunications system is Wireless Switching Center ("WSC") 120, which may also be known as a Mobile Switching Center ("MSC") or a Mobile Telephone Switching Office ("MTSO"). Typically, Wireless Switching Center 120 is connected to a plurality of base stations (e.g., base stations 103-1 through 103-5) that are dispersed throughout the geographic area serviced by the system. Additionally, Wireless Switching Center 120 is connected to local- and toll-offices (e.g., local-office 130, local-office 138 and toll-office 140). Wireless Switching Center 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal, which is connected to the system via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially-distinct areas called "cells." As depicted in FIG. 1, each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on terrain topography. Typically, each cell contains a base station, which comprises radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with WSC 120.
For example, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to WSC 120. Upon receiving the information, and with the knowledge that it is intended for wireless terminal 101-2, WSC 120 then returns the information back to base station 103-1, which relays the information, via radio, to wireless terminal 101-2.
To relay information, the radio modulates the information onto a RF carrier signal in accordance with the particular modulation scheme of the wireless system (e.g., time-division-multiple-access, code-division-multiple-access, etc.). The modulated output RF signal from the radio is a very low power signal that requires amplification for transmission from base station 103-1 to wireless terminal 101-2.
A feedforward multicarrier linear RF power amplifier can be used to amplify the output signal from the radio. In fact, such an amplifier can usually amplify all of the RF carrier signals in use within a given cell. The design and operation of linear amplifiers are known in the art. See, for example, U.S. Pat. No. 5,304,945, which is incorporated by reference herein.
Unfortunately, conventional feedforward multicarrier linear RF power amplifiers are very complex and costly, both to design and manufacture. And, each application requires a custom design dictated by a variety of system requirements. Conventional feedforward multicarrier linear RF power amplifiers have been designed using a combination of RF circuits, analog control circuits and digital control circuits. A simplified schematic of linear amplifier circuit 200 is shown in FIG. 2. As depicted in FIG. 2, linear amplifier circuit 200 includes several splitters (202, 220), gain & phase control circuitry (204, 224), couplers (214, 216, 222, 228), delay circuitry (210, 218), a correction amplifier (226), pre-distortion driver circuitry (206), the main amplifier (208) and processor control circuitry (212).
The various circuits of a conventional linear amplifier are typically interspersed within a large housing that is designed to support the weight of the main amplifier, dissipate heat and prevent RF from radiating to the external environment. Additionally, the various individual circuits are housed in metal boxes or "clam shells" to provide RF isolation.
It would be desirable to reduce the cost and complexity of such amplifiers. Modularization is a technique that may be used to achieve such ends. When modularizing, components or circuits of a device are segregated into modules based on one or more underlying criteria. It will be appreciated that, as a complex electronic device comprised of a myriad of circuits, there are potentially numerous ways to modularize a feedforward multicarrier linear RF power amplifier. For example, modularization can be based on segregating components that generate noise from components that are sensitive to noise, or segregating components that generate heat from non heat-generating components, or segregating components requiring access for initial or periodic adjustment from those that do not, or segregating components based on weight or size considerations, to mention just a few.
Such varied approaches will yield varied results in terms of the utility of the modularized amplifier. A desirable approach is one that reduces the cost of designing and manufacturing the amplifier, that reduces the time to deliver the amplifier for a specific service, and one that simplifies field servicing of the amplifier.